With increase in recognition of recycling usage of biological resources, a lot of kinds of organic wastes have recently been composted and reduced to the earth as resource. Livestock excreta which is feces of the livestock and food wastes such as food scraps (hereinafter these are collectively referred to as “feces of the livestock and the like”) that are most expected to be composted and/or resourced, often has high moisture, or so-called in a quagmire state, at the time of generation. For such feces of the livestock and the like, there are difficulties, such as that oxygen is hardly introduced inside the feces of the livestock and the like because of the quagmire state, that the biochemical reaction by the ordinary microbial degradation is difficult to occur, and that the feces of livestock and the like are difficult to be composted. As a result, conventionally, a method which reduces a water content ratio in order to easily take in the oxygen inside the feces of the livestock has been adapted.
As one of the means to reduce the water content ratio, there is a method to provide heat energy, air distribution and the like to the organic waste. However, such a method is not realistic due to an issue of the cost. In addition, as another means, as in the case of the feces of the livestock which are the livestock excreta, there is a method to mix agricultural by-products, such as sawn wood, rice straws, rice husk and the like, with the organic waste. This method reduces the moisture contained in the organic waste and, as a result, to ease the airflow to promote the biochemical reaction by microbial degradation. However, the agricultural by-products may be difficult to procure in some regions, or the cost for procuring the agricultural by-products may increase. Moreover, even when the agricultural by-products can be obtained, the cost may further increase due to the additional processing of the agricultural by-products. Furthermore, in this method, there is a difficulty that the mixture of such agricultural by-products causes an increase in costs as the total amount of treatment increases.
It has been considered to reduce the volume of the organic waste and return to the natural world without composting and resourcing the organic waste. However, even in that case, the water content ratio must be decreased for the organic waste in the quagmire state. This results in the problem similar to the above. Moreover, when the water content ratio of the organic waste in the quagmire state is simply lowered and dried, the reaction for composting the waste by the microbial degradation does not occur. Therefore, the dried organic waste would return to the original organic waste in the quagmire state when returned to the natural world. Moreover, in this method, cost for sewage process similar to those for human excreta cannot be incurred.
On the other hand, patent document 1 proposes a method of treating the waste to achieve volume reduction or carbonization of the waste by pressurizing and heating up the waste including food scraps in a steam kiln. Patent document 2 proposes a method of controlling the supplied amount of air in a gas furnace so that amount of carbon monoxide, which is generated by partial combustion of municipal waste, is maximum. Patent document 3 discloses a dry method of organic products and the like that monitors concentration of carbon monoxide included in an atmosphere gas, which contacts to a dray product, and that maintains the concentration of carbon monoxide at a predetermined value over 10 ppm and below 100 ppm. Patent document 4 proposes a mixture method of kitchen waste performing wet combustion treatment process. The wet combustion treatment process produces slurry by mashing kitchen waste and mixing the mashed kitchen waste with sewage water, pressurizes the slurry by high-pressure pump and feeds high-pressure gas including oxygen or high-pressure air into the slurry, and heats up the pressurized slurry by temperature at which kitchen waste in the pressurized slurry is oxygenized. Patent Document 5 proposes subcritical water degradative treatment method that executes subcritical water degradative treatment at reaction temperature of 130-374 degrees Celsius and reaction pressure over saturated vapor pressure of the reaction temperature.